The woman who triggered the investigation that led to the resignation of CIA chief David Petraeus threw lavish parties for top military brass – and also racked up debt. NBC's Kristen Welker reports.

By NBC News staff

The FBI agent who was asked by Jill Kelley to look into disturbing emails she received was a friend of hers and never had a further part in the investigation, a senior law enforcement official said Tuesday.

The official says the FBI agent had met Kelley many months before she complained to him about the threatening emails -- allegedly sent by Paula Broadwell, Gen. David Petraeus’ biographer and a woman with whom he is believed to have had an affair.

The agent sent Kelley a photo of himself with no shirt, "as a joke, a gag" at least six months before she began receiving the troubling emails, the official said. There is, the official said, no indication that the relationship between the two was anything more than a friendship.

But the official says that after Kelley came to the agent with her complaint, he faded from the picture and was not in on the investigation. Then agents discovered the shirtless photo in her e-mails, which was reported to his supervisors, resulting in an internal investigation into whether he acted inappropriately.

He's the same agent who contacted House Republicans in October to complain that the investigation was stalled. But, the official said, the agent was far out of the loop and had no idea all of the investigative activity still under way at that point.

House Majority Leader Eric Cantor’s office called the FBI on Oct. 31 asserting that it had heard from an FBI agent who raised concerns that the matter was being covered up or not being taken seriously.

Those who know the two women at the center of General David Petraeus' affair scandal are speaking out. Jill Kelley's brother says she is "dedicated" to her husband, while Paula Broadwell's friend calls her "a pretty great person." NBC's Kristen Welker reports.

"I was contacted by an FBI employee concerned that sensitive, classified information may have been compromised and made certain (FBI Director Robert) Mueller was aware of these serious allegations and the potential risk to our national security,” Cantor said in a statement.

Cantor's office was told that the case was being actively investigated by the FBI, and so it would have been wrong for the FBI or Justice Department to inform higher-level officials in the administration about the probe earlier -- because they were unsure at that point what they were dealing with. In the end, according to multiple officials, investigators determined there was no criminal wrongdoing.

The agent provides yet another link to Kelley, who has become a central figure in the scandal that led to the resignation of Petraeus over his affair with Broadwell: Her complaint to the FBI kicked off the investigation, and her emails with another major military figure, Gen. John Allen, have led to an investigation over allegations of “inappropriate” emails between Allen and Kelley. Allen replaced Petraeus as commander in Afghanistan last year.

The emails between Allen and Kelley do not signify the two had an affair, a defense official told NBC News on Tuesday. “There was no affair,” said the official, who spoke on condition of anonymity. The emails in question could be misconstrued, the official said, predicting that the investigation will prove Allen’s innocence.

Ret. Col. Jack Jacobs weighs in on the scandal that has ensnared former CIA chief David Petraeus and Gen. John Allen, telling TODAY's Savannah Guthrie that Allen has a stellar career and great reputation but he "wouldn't be surprised" if his NATO nomination was withdrawn.